1. Field of the Invention
The present invention relates to an ADSL system for transferring an analog audio signal and a high-speed digital data through one subscriber line, and more particularly to an ADSL system capable of transferring the same without using POTS splitter.
2. Description of the Related Art
FIG. 3 is a view showing an example of the structure of the conventional ADSL (Asymmetric Digital Subscriber Line) system. As illustrate in FIG. 3, in the conventional ADSL system, high-speed digital data transferred from and to a high-speed data apparatus 31 on a subscriber side, after being modulated and demodulated by an ADSL modem 32, is transferred from and to a station through the same subscriber line 35 by an integrated separator 33, together with an analog audio signal sent and received through an analog telephone 34 on the subscriber side, in such a state that they are integrally divided by the frequency. On the station side, after being modulated and demodulated by an ADSL modem 37, the high-speed digital data from a high-speed digital data network 36, together with an analog audio signal sent and received through an analog telephone network 39, is transferred from and to the subscriber through a subscriber line 35 by the an integrated separator 38, in such a state that they are integrally divided by the frequency.
The conventional ADSL system thus constituted must be provided with an integrated separator (filter) for separating an analog audio signal and high-speed digital data, called a POTS (Plain Old Telephone Service) splitter, on the both sides of a station and a subscriber. Therefore, the conventional system has the following problems.
At first, since the POTS splitter consists of coils and a condenser of large size, especially, the station side has to accommodate a large number of subscribers, thereby increasing the volume thereof.
At second, in order to set a POTS splitter on a subscriber side, a constructor has to go to the subscriber's site to do setting and wiring works. In other words, it is difficult for a subscriber to set the splitter and he or she must pay the labor costs for dispatching a constructor.
At third, when setting a POTS splitter on an existing analog telephone network, because the POTS splitter is directly connected to a subscriber line, there is a fear of disturbing the quality of the subscriber line that has been in the ordinal state. Therefore, it is necessary to optimize the design of the POTS splitter not to disturb the quality of the subscriber line.
At fourth, terminal impedance of a subscriber line varies depending on each country, optimization of the POTS splitter requires each design suitable for the terminal impedance of each country, thereby increasing the development costs for arrangement depending on each country.